# Voltage/Frequency Control MCQ Questions & Answers

Voltage/Frequency Control MCQs : This section focuses on the "Voltage/Frequency Control". These Multiple Choice Questions (MCQs) should be practiced to improve the Voltage/Frequency Control skills required for various interviews (campus interview, walk-in interview, company interview), placement, entrance exam and other competitive examinations.

Question 1

Armature reaction is cross-magnetizing in nature due to a resistive load in the synchronous generator.

A. True
B. False

Question 2

Armature reaction is purely demagnetizing in nature due to a capacitive load in the synchronous motor.

A. True
B. False

Question 3

Calculate the minimum value of the active power in the cylindrical rotor synchronous machine? (Eb represents armature emf, Vt represents terminal voltage, ? represents rotor angle, X represents reactance)

A. Eb×Vt×sin?÷X
B. 0
C. Eb2×Vt×sin?÷X
D. Eb×Vt÷X

Question 4

Calculate the power factor if the power angle is 45°.

A. 0.707
B. 0.407
C. 0.608
D. 1

Question 5

Calculate the reactive power in a 451.26 ? resistor.

A. 1 VAR
B. .6 VAR
C. 0 VAR
D. .9 VAR

Question 6

Calculate the reactive power in a 725.45 ? resistor.

A. 122.1 VAR
B. 261.1 VAR
C. 0 VAR
D. 199.7 VAR

Question 7

Calculate the value of the duty cycle if the system is on for 1 sec and off for inf sec.

A. 0
B. 0.89
C. 0.148
D. 0.46

Question 8

Calculate the value of the short circuit ratio if Voc=78 V, Isc=15 A with field current = 5 A.

A. 5.2
B. 4.8
C. 3.2
D. 1.8

Question 9

Cylindrical pole machines are less stable than salient rotor machines.

A. True
B. False

Question 10

SCR determines the stability of the synchronous machine.

A. True
B. False

Question 11

The phase difference between voltage and current in the purely inductive coil.

A. 20°
B. 90°
C. 40°
D. 88°

Question 12

The slope of the I-V curve is 180°. Calculate the value of resistance.

A. inf ?
B. .81 ?
C. 45 ?
D. 41.2 ?

Question 13

The unit of area is m2.

A. True
B. False

Question 14

Calculate the minimum value of the active power in the cylindrical rotor synchronous machine? (Eb represents armature emf, Vt represents terminal voltage, δ represents rotor angle, X represents reactance)

A. Eb×Vt×sinδ÷X
B. 0
C. Eb2×Vt×sinδ÷X
D. Eb×Vt÷X

Question 15

Calculate the reactive power in a 451.26 Ω resistor.

A. 1 VAR
B. .6 VAR
C. 0 VAR
D. .9 VAR

Question 16

Calculate the reactive power in a 725.45 Ω resistor.

A. 122.1 VAR
B. 261.1 VAR
C. 0 VAR
D. 199.7 VAR

Question 17

The slope of the I-V curve is 180°. Calculate the value of resistance.

A. inf Ω
B. .81 Ω
C. 45 Ω
D. 41.2 Ω